capillary force
(rus. капиллярная сила otherwise капиллярные явления)
—
force caused by capillary phenomena which occur at the curved surface of the interface between matter in the liquid and solid or gas phase.
Description
The surface curvature of a liquid at the interface with a gas phase occurs as a result of surface tension of the liquid, which tends to reduce the surface and shape the limited volume of the liquid to a point with the lowest surface tension forces potential. The surface tension forces create additional pressure (capillary pressure) under the interface that can be calculated using Laplace’s equation:
,
where
is the surface tension, and 
is the average radius of surface curvature.
In sufficiently large masses of liquid, the surface tension is compensated by the force of gravity, therefore the capillary phenomena are observed primarily for liquids enclosed in narrow channels (capillaries) and porous media.
In a narrow channel the liquid to gas interface takes a curved shape (meniscus), that can be convex if the liquid does not wet the capillary walls and concave if it does. A convex meniscus creates positive pressure above its surface, while a concave meniscus creates negative pressure (vacuum). The latter phenomenon causes liquid to flow into the capillaries with wetted walls, even against gravity, which plays an important role in many biological processes. Capillary phenomena in porous media are responsible for the distribution of ground water, and soaking up of liquids by fabrics or other fibrous materials (wick effect). When two rough wetted surfaces interact, meniscus of liquid occur near local contact points, giving rise to capillary adhesion.
, where
is the surface tension, and is the average radius of surface curvature. In sufficiently large masses of liquid, the surface tension is compensated by the force of gravity, therefore the capillary phenomena are observed primarily for liquids enclosed in narrow channels (capillaries) and porous media.
In a narrow channel the liquid to gas interface takes a curved shape (meniscus), that can be convex if the liquid does not wet the capillary walls and concave if it does. A convex meniscus creates positive pressure above its surface, while a concave meniscus creates negative pressure (vacuum). The latter phenomenon causes liquid to flow into the capillaries with wetted walls, even against gravity, which plays an important role in many biological processes. Capillary phenomena in porous media are responsible for the distribution of ground water, and soaking up of liquids by fabrics or other fibrous materials (wick effect). When two rough wetted surfaces interact, meniscus of liquid occur near local contact points, giving rise to capillary adhesion.
Illustrations
|
Behavior of a liquid in a capillary tube. |
Authors
- Irina G. Goryacheva
- Alexey G. Shpenеv
Sources
- Capillary action // Wikipedia, the free Encyclopedia. — www.en.wikipedia.org/wiki/Capillary_action (reference date: 12.12.2011).
- Capillary phenomena / / Chemical encyclopedia (in Russian). V. 2. — M.: Sovetskaja ehnciklopedija, 1990. P. 310–311.
- Capillary phenomena / / Great Soviet Encyclopedia (in Russian) 3rd ed., 1969–1978.